In general, the function of a laminating adhesive is to join together different or similar substrates, e.g., polyethylene, polypropylene, polyester, polyamides, metal, paper or cellophane to form composite films used for many different purposes. A suitable laminating adhesive is expected to provide excellent bonds on numerous substrates with only a small application of adhesives. Large amounts of such laminates are used in the packaging industry, especially in making food packaging. Due to environmental, health and safety reasons, it is preferred that the adhesives be solvent free.
Aqueous linear or crosslinked aqueous polyurethane dispersions may be used in a wide range of commercial applications such as coatings and adhesives as shown in several patents including U.S. Pat. Nos. 5,147,926, 5,610,232, 5,637,639, 5,608,000 and 5,334,690.
U.S. Pat. No. 5,147,926 disclose crosslinkable aqueous polyurethane dispersion having long shelf life and containing polyurethanes which have carbonyl and polyhydrazides and their use for the preparation of printing inks.
U.S. Pat. No. 5,01,881 is directed to aqueous coating composition comprising aqueous acrylic resin and urethane resin emulsion in the absence of a crosslinking agent. The coatings are used for plastic substrates.
U.S. Pat. No. 5,281,655 is directed to aqueous coating composition for metallic and plastic substrates. The composition comprising a urethane resin emulsion, a resin for use in aqueous coating composition and a hydrophobic melamine resin as a crosslinking agent. There is no disclosure regarding the use of the composition as a laminating adhesive.
U.S. Pat. No. 5,281,655 is directed to an aqueous polyurethane dispersion and its use in the manufacturing of laminate structures. The adhesive comprises a prepolymer comprising a reaction product of an aliphatic polyfunctional isocyanate compound, and an acid functional polyol component, wherein said prepolymer is dispersed in water in the presence of a dispersion stabilizing amount of a tertiary amine.
The present inventors have found an alternate stabilizer for use in dispersing a polyurethane prepolymer in water that is surprisingly effective while not adding to VOCs (volatile organic contents) of the dispersion.